I know this would be a ripoff to other trainers, but it works.
any kinda of music would do, but it would have to be non copyrighted music, midi,wave, ect.
Probably could also do a thing on the website accepting non copyrighted midi or short wave music from people and then do voting on the music.
also on another note, version checking on game exec, to make sure trainer is compatible.
Although some trainers will have a name of the person who converted a tune or made it up on those sites, to show respect.
As for CH trainers it isn't needed, are people really going to sit for about a minute or two to listen to it? Nahh they are more interested in using the trainer and playing a game :P